Atrial fibrillation originating from rapid firing foci in the superior vena cava is rare. Its electrophysiological features and catheter ablation techniques are described in this report. A decapolar catheter was positioned in the superior vena cava to map the origin of the atrial fibrillation in a 39-year-old female patient who had a 3-year history of symptomatic atrial tachycardia and fibrillation. Intracardiac mapping showed rapid firing foci in the anterior wall of the superior vena cava (SVC), 2.0 cm above the SVC'right atrium junction. During tachycardia, the focal electrogram from SVC was 55 msec earlier than the P waves on body surface ECG. Radiofrequency catheter ablation successfully abolished SVC potentials, resulting in a SVC'atrium conduction block. There was no recurrence of atrial arrhythmia after a 14-month follow-up. Rapid activities from the muscle sleeves in the SVC may cause atrial fibrillation. Such a focal atrial fibrillation can be eliminated by isolating the arrhythmogenic SVC with radiofrequency catheter ablation.